Portable electronic devices, such as handheld computers, laptops, and wireless telephones, are proliferating rapidly for a wide variety of consumer, business and military applications. As their use continues to expand, consumers of all types desire longer power-on times and a continuously expanding set of functions for them. In order to accommodate this, a corresponding increase in the demand for portable electrical power generation and supply needs to be met.
The limited size of these devices places a limit on the size of batteries that can be used to power them. This, in turn, places a natural limit on the amount of power conventional batteries can produce. In order to overcome this potential shortfall in portable power for the future, other sources of power generation for portable electronic devices have to be pursued.
Electrochemical fuel cells have a well-recognized potential to revolutionize energy production, for both large-scale and small-scale applications. However, as is well known, this potential cannot be realized until simple, cheap and energy efficient means for hydrogen fuel production becomes available. To this end, recent advances in micro-fabrication have led to the development of compact chemical micro-reactors for various small-scale applications, such as on-demand production of hydrogen or other chemical fuels useful for portable fuel cell technologies. In addition to the favorable properties of rapid heat and mass transport, the miniaturization of chemical reactors offers higher productivity rates due to the fast, non-equilibrium surface chemistry properties of the miniaturized reactor.
The above-mentioned size limitations pertinent to portable electronics, coupled with the attractive potential for process intensification associated with micro-scale technologies, led to several attempts to design, fabricate, and test micro-machined chemical reactors for portable hydrogen fuel generation. The most notable examples are those from the Pacific Northwest National Laboratory (PNNL), Motorola Energy Technology Labs, Sanyo Corp., Lehigh University, and Innovatek, Inc. These groups each focused on single reaction systems that attempt to convert known, conventional, large-scale, hydrogen production processes to micro-scale applications. In particular, PNNL has explored catalytic partial oxidation micro-reactors, whereas the other groups have developed steam-reforming micro-reactors.
A PNNL fuel reformer is depicted in FIG. 1. It has the advantage of a sandwich-like design that is complimentary with micro-electro-mechanical systems (MEMS) planar (i.e. two-dimensional) fabrication due to easy connection of sub-systems through common through-holes and structure lamination. However, such a system functions in a sequential series of stages for mixing, vaporization, combustion, and fuel reforming. This staging results in an increased operating temperature, a higher pressure drop, a larger reactor size, and requires the use of a complex network of fluidic channels and heat exchangers. To date, previous efforts have also failed to overcome certain limitations including operating at reduced reactor “skin” temperatures, which is required for safe portable power generation.
Accordingly, there is a need for an integrated micro fuel processor for hydrogen production and portable power generation that addresses certain problems of existing technologies.